In recent years, many mobile devices are found using cloud computing, and an account on a network is required for using the devices. The account is a right for a user to log into a specific device and the like, and information for specifying an account is referred to as account information. For example, the account information includes a combination of an ID for identifying a user and a password. Various types of information, which is used and generated in the mobile device, are stored on the network, as account-related information associated with the account information. An example of the account-related information includes e-mails, schedules, contact information, configuration files, music, videos, and the like. By storing the account-related information on a network with being associated with the account information, the same environment can be restored when the user changes the mobile device. Further, various types of data and environment settings may be shared with another mobile device or a device such as a personal computer (hereinafter, PC). Furthermore, by holding a plurality of accounts and setting an environment for each account, the user may easily change the environment settings of a device by switching the account.
In many mobile devices using accounts, the account information provided by the user and the account-related information acquired from the network are stored in the device. Therefore, if the user loses the device, there is a risk of that a third party views the account information and the account-related information.
Patent Document 1 discloses a technology of monitoring a state of a mobile device and automatically deleting data which is pre-designated by the user when the state meets a pre-designated condition. The user sets three conditions in advance as follows: 1) an upper limit time to allow the continuation of a state with respect to each of various states of the mobile device such as a power-off, 2) operations of the mobile device which trigger the process of data deletion, and 3) data to be deleted. The mobile device disclosed in Patent Document 2 checks whether or not the respective states designated in 1) continue longer than the upper limit time when any operation designated in 2) is performed, and deletes data designated in 3) when any state continues longer than the upper limit time.
Patent Document 2 discloses a technology of monitoring two points including 1) whether a user is present near a device, and 2) whether or not a radio wave condition is out of range, and of protecting data according to the monitored status by processing of locking access to data in the device, saving data to an external device, or deleting data.
As a technology aimed at protecting data in addition thereto, there are Patent Documents 3 to 6. Further, Patent Documents 7 and 8 disclose technologies of managing accounts through the use restriction of an account or automatic deleting in a server which manages accounts. Patent Document 9 discloses a technology of lowering a security level of data in accordance with the passage of time, or the like.